Granular filter medium

ABSTRACT

A method for filtering contaminants from suspension in liquids by utilizing, as a filter medium, granulated shells of black walnut (Juglans nigra L.).

United States Patent 91 Hirs [4 1 Dec. 25, 1973 [52] US. Cl. 210/80,210/500 [51] Int. Cl B0ld 23/24 [58] Field of Search 210/40, 67, 500,

[56] References Cited UNITED STATES PATENTS 3,680,699 8/l972 MacPherson210/503 X 3,562,153 2/i97l Tully et al 2l0/40 X 3,550,774 12/1970 Hirset al. 210/67 Primary Examiner-Samih N. Zahama Assistant Examiner-RobertH. Spitzer Attorney-Hiram P. Settle, Jr.

[57] ABSTRACT A method for filtering contaminants from suspension inliquids by utilizing, as a filter medium, granulated shells of blackwalnut (Juglans nigra L.).

1 Claim, No Drawings GRANULAR FILTER MEDIUM BACKGROUND OF THE INVENTIONApplicant has earlier proposed in his U.S. Pat. Nos.

3,557,955 and 3,550,774 a new and novel type of 5 deep bed filterwherein synthetic polymeric materials in finely granulated form areutilized as the filter media.

The utilization of synthetic polymeric materials, such as polyvinylchloride materials, is preferred because of the combination of thenecessary physical characteristics of such materials. For example, themethod and apparatus disclosed in U.S. Pat. No. 3,550,774 cleanses thefilter medium by placing the mixture of medium and earlier removedcontaminants in a slurry and then subjecting this slurry to a violentwashing action, i.e., flowing the slurry past a perforate scrubbingelement. Any practical filter medium for utilization in such a methodmust be light (preferably having a specific gravity of 1.55 or less),strong (having a modulus of elasticity of 40,000 psi or greater) andnon-abrasive (so as not to wear away the perforate scrubbing element).

These requirements of the filter medium eliminate from consideration thecommon granular filter media, such as sand, anthracite, and activatedcarbon. Many other materials, particularly synthetic polymericmaterials, are eliminated because of their high cost.

Many natural materials have been investigated and found wanting becauseof their inherent lack of the strength necessary to withstand theslurrying and violent cleansing of the media.

BRIEF DESCRIPTION OF THE INVENTION It has been found that the granularshells of black walnut (Juglans nigra L.) possess a unique combinationof properties which makes it fully acceptable as a filter medium forutilization in the method and apparatus disclosed in applicants priorU.S. Pat. Nos. 3,550,774 and 3,557,955 or in similar apparatus ormethods where a light, strong, and not too abrasive or brittle filtermedium is necessary.

OBJECTS It is, therefore, an important object of the present inventionto provide a filter medium consisting essentially of a bed of granulatedshells of black walnuts.

Another important object of the present invention is the provision of amethod of filtering contaminant particles from a liquid by passing thecontaminated liquid through a bed of granulated shells of black walnuts.

Yet another, and no less important, object of the present invention isthe method of filtering contaminant particles from a liquid by passingthe liquid through a bed of granulated shells of black walnuts, andcleansing the contaminant particles from the bed by violently slurryingthe bed and the particles and passing the slurry past a perforateseparating element through which a part of the slurry containingcontaminant particles is withdrawn.

DETAILED DESCRIPTION OF THE INVENTION As above explained, the presentinvention proposes a filter medium for utilization in the apparatus andmethods set forth in applicant's earlier U.S. Pat. Nos. 3,550,774 and3,557,955, and the disclosures of the apparatus and methods set forth inthese two prior patents are included herein by reference. To utilize thefilter bed of the present invention, granulated shells of black I walnut(J uglans nigra L.) are simply substituted for the synthetic polymericmaterials disclosed in said earlier patents. The apparatus remains thesame as disclosed in said patents and the methods of operation remainthe same.

The unique properties of the granulated shells of black walnut allowthis complete substitution, and the shells are preferably utilized in asize ranging from about 20 to 60 US sieve number. The shells of blackwalnuts are light in weight, with a specific gravity of 1.3 to 1.4. Theshells also are relatively strong, having a modulus of elasticity of170,000 psi, and the shells are relatively non-abrasive when compared tosand or anthracite. This last property is somewhat suprising in view ofthe common use of walnut shells as a blasting grit for metal finishing.However, black walnut shells are utilized as soft grit which does notcause pitting of the metal part to be cleaned.

To illustrate the utilization of granular black walnut shells as afilter medium, the following table is presented. In obtaining thefigures in this table, liquid containing a standard test dirt consistingof Fe O dirt in the indicated amount was passed through 12 inches of 20to 50 mesh granular black walnut shells. The dirt was added at a rate of250 mg per liter. The filter flow rate was 10 gallons per minute persquare foot of crosssectional area of the shells. The following resultswere obtained:

Pounds of Gallons of dirt added filtered per cubic Filter effluentclarity liquid foot of media mg/l 20 0.5 0.24 40 1.0 0.36 60 L5 3.2 2.09.9 2.5 14.5

Generally speaking, the above table illustrates that granular blackwalnut shells have a dirt holding capacity which is substantiallyequivalent to that of silica sand.

Other favorable characteristics of black walnut shells when utilized asa filter medium are that they are oil and water resistant, they have ahardness in Mohs of 3, and are for all practical purposes chemicallyinert. Also, granular black walnut shells are commerically available inall practical mesh sizes for use in deep bed filtration at a cost whichis about one-sixth the cost of many inexpensive plastic materials.

I claim:

1. The method of filtering particulate contaminants from a liquidcomprising;

flowing the contaminated liquid through a filter bed of granulatedshells of black walnuts (J uglans nigra L.); terminating the flow of thecontaminated liquid after at least a portion of the contaminants havebeen retained in said filter bed; and cleansing said filter bed byviolently and turbulently backwashing at least a part of said filter bedhaving contaminants therein over a perforated element, and withdrawingat least a portion of said contaminants through said perforate element.

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